The role of dietary factors in cancer prevention has been assessed in animal experiments, in human epidemiologic studies, and, most recently, in prevention trials. For many of these agents, however, information is incomplete concerning their safety, toxicity, dose, form, bioavailability, pharmacokinetics, and mechanism of action. To further define these parameters in humans, a cooperative research effort between the Beltsville Human Nutrition Research Center (BHNRC), U.S. Department of Agriculture, and the CPSB, DCPC, is being conducted. The overall goal of this collaborative effort is to obtain further information on potential cancer preventive agents. Initial efforts have focused on 3 nutrients which have shown the most promise for cancer prevention -- selenium, fat, and beta-carotene. A study of the kinetics of a single, oral dose of two forms of selenium in the fasting and non-fasting state was conducted in the first year. Future activities will evaluate the safety/toxicity of selenium and form of ingestion among persons residing in seleniferous areas. Our first study of fat focused on potential mechanisms of action and will assist us in the evaluation of the relation of type and amount of dietary fat to hormonal status, bile acid metabolism, and fecal mutagenic active in premenopausal women. Subsequent evaluations will examine the relation of dietary fat and fiber to fecal mutagens in men, focusing on the prominent mutagen, fecapentaene. Beta-carotene studies are examining the plasma carotenoid response to single- and long-term ingestion of beta-carotene from either a capsule or from selected vegetables.